This roofing calculator estimates your roof’s surface area from the house footprint and roof pitch, then works out roofing squares, shingle bundles and underlayment rolls, with a waste allowance. Add a price per square from your quotes to estimate the cost.
How roof area is calculated
- Measure the house length and width, including the roof overhangs.
- Multiply by the pitch multiplier: √(1 + (rise ÷ 12)²). A steeper roof has more surface than its footprint.
- Divide by 100 to get squares; one roofing square covers 100 sq ft.
- Add waste: about 10% for a simple gable roof and 15% or more for hip roofs or roofs with valleys and dormers.
Pitch multipliers
| Pitch | Angle | Multiplier |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 5/12 | 22.6° | 1.083 |
| 6/12 | 26.6° | 1.118 |
| 7/12 | 30.3° | 1.158 |
| 8/12 | 33.7° | 1.202 |
| 9/12 | 36.9° | 1.250 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45.0° | 1.414 |
Worked example
A 50 × 30 ft footprint with a 6/12 pitch has a roof area of 1,500 × 1.118 ≈ 1,677 sq ft, or 16.8 squares. With 10% waste and 3 bundles per square, you would buy 56 bundles of shingles.
How to find your roof pitch
From the attic or a ladder, hold a level horizontally against the rafter or roof, measure 12 inches along the level, then measure straight up to the roof. That height is the rise per 12 inches.
Frequently asked questions
How many bundles of shingles are in a square?
Most architectural and 3-tab shingles come 3 bundles to a square, but some heavier shingles need 4 or 5. Check the packaging.
How much extra roofing should I order?
About 10% for simple gable roofs and around 15% for hip roofs or roofs with many valleys, dormers or angles.
Can I measure my roof from the ground?
Yes. Measuring the footprint with overhangs and applying the pitch multiplier avoids climbing on the roof.
What is the minimum pitch for shingles?
Asphalt shingles generally need at least 2 in 12, with extra underlayment below 4 in 12. Follow the manufacturer’s instructions.
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Last reviewed: October 2026. For information only; results are estimates; check important figures with a professional.